/Engine/Source/Developer/TextureFormat/Public/Interfaces/ITextureFormat.h
InLinearSurfaces must have the necessary input mips for the mip level - i.e. for a packed mip tail, InMipIndex is the index of the top mip of the tail, and InLinearSurfaces must have all the source mips for the entire tail.
[FSharedBuffer](API\Runtime\Core\Memory\FSharedBuffer) ProcessMipLevel ( const [FEncodedTextureDescription](API\Developer\TextureFormat\Interfaces\FEncodedTextureDescription) & InTextureDescription, const [FEncodedTextureExtendedData](API\Developer\TextureFormat\Interfaces\FEncodedTextureExtendedData) & InExtendedData, [TArrayView](API\Runtime\Core\Containers\TArrayView)< FMemoryView > InLinearSurfaces, int32 InMipIndex ) const